Process of softening rubber



Patented Dec. a1, 1926.

CHARLES P. HALL, or ARRoN, onro.

rRocRss F sor'rENmo RUBBER.

R0 Drawing.

This invention relates to a new and improved process of softening rubber, the ob- ]ect of the invention being to improve upon existing methods and products as will be 6 explained herein.

In the preparation of rubber stocks, it is customary to use certain softening agents which improve the milling of the rubber and impart certain beneficial qualities to the IU vulcanized product. A number of these softening agents have been employed and suggested. Perhaps the most widely used and satisfactory substance known prior to my invention is pine tar which has many valuable properties, but also tain well known disadvantages.

I have made a very considerable study of various" softening agents and their properties, with a view to improving upon pine tar or any other agent for this purpose, and, as a result, I have found that a certain asphalt residue of the cracking still obtained in the cracking of crude petroleum in a certain manner, possesses properties superior to those of any softenin agent heretofore known. 1 Such product is derived by the removal by distillation, preferably with steam, of lighter portions of tar o'r residue resulting from the cracking or conversion under pressure of hydrocarbon oils heavier than gasoline into gasoline; for example, a product such as that described in the Burton Patent No. 1,553,847, granted September 15, 1925.

The. substance referred to possesses may 3 advantages over otherf softeners, asphalts or petroleum residues. It is'a syrupy liquid having approximately the consistency of molasses. It softens the stock and renders .itmore plastic than an equivalent weight of pine tar, thus shortening the time of milling. Taking 100% as a standard of softening with pine tar, the material herein contemplated willgive a plasticity of 115% as compared with approximatel 83% for mineral rubbers. No odors or ot er physical inconveniendes occur in the milling of the rubber, and it posseses many other advantages.

The substances referred to has the following analysisi possesses cerelongation being 60 cm.

Application filed July 23, 1925. Serial No. 45,712.

' Soluble in CS not less than 99.

Soluble-in CCL, not lessthan 98. Soluble in hexane, not less than 75. Spec. gravity at 60F. not less than 1.06. Spec. gravity at 77 F. not less than 1.05. Fixed carbon, less more than 14. Flash test (ASTM), F. not more than 5.

Paraffin scale, not more than 2. Visc. at 212 F. (Engler) 5 to 7. Visc. at 212 F. (Saybold universal) 180 so to 250- Loss on evaporation, 50 grams, at 325 F. for-5hr. not over 3.0.

lVhen evaporated at a, temperature not exceeding 500 F. until the residue has a penetration of 100 at 77 F., the percent of such residue shall not be less than 75, and it shall have a ductility at 77 F. of not less than 100 cm., when tested in a standard ductility machine usin the Dow mold, the rate of 7 er minute. In mixing it with rubber, it is added to the batch upon the mill and may be used with any usual or preferred ingredients and in. any suitable roportion. The material 7 may be compoun ed, for example, with rubber, zinc oxide, carbon black, or other pigment, sulphur and an accelerator, and the resulting vulcanized compound will have superior abrasion resisting properties, great- 30 er elongation and superior tensile strength over compounds using mineral or vegetable softeners. By the use of the material, the time for curing a non-blooming stock will be lowered and a more uniform tensile strength will be obtained over a longer period of cure. Itgives superior aging char acteristics than those obtained by the use of mineral or vegetable oils as softeners and reduces the impairment and loss of tensile strength due to the oxidization and to the presence of active accelerating mediums in the rubber. The resulting compound is particularly adaptable for use as a tread stock for pneumatic tires, although its use is not I necessarily so restricted.

It has been found that by the use of this material in the compounding of rubber the various advantageous results set forth and others are obtained.

What I desire to claim is: The process of softening rubber for milling and compounding which comprises adding to the rubber a softenin agent having the following analysis: solu 1e in CS spec. gravity at 77 9 F. not less than 1.05;

} fixed carbon, not more than 14; flash test (ASTM), deg. F. not more than 375; paraffin scale, not more than 2; visc. at 212 F. (Engler) 5 to 7; vise. at 212 F. (Saybolt 15 universal) 180 to 250; loss on evaporation, 5O grams, at 325 F. for 5 hr. not over not less than 99; soluble in 0C1 not less 3 0 than 98; soluble in hexane, not less than 75; spec. gravity at 60 F. not less than 1.06;

CHARLES P. HALL. 

